The difference between breast cancer chemotherapy EC regimen and AC regimen includes different drugs and different applied conditions. 1. Different drugs: EC regimen of breast cancer chemotherapy refers to the combined application of cyclophosphamide and epirubicin. Breast cancer chemotherapy AC regimen mainly refers to the two-drug combination regimen composed of anthracycline epirubicin and cyclophosphamide. 2. Different applied conditions: EC regimen for breast cancer chemotherapy is a kind of adjuvant regimen applied to the treatment of lymph node-positive breast cancer patients in intravenous treatment. Breast cancer chemotherapy AC regimen is mainly used in adjuvant chemotherapy for breast cancer or metastatic breast cancer. The chemotherapy regimen of breast cancer should be selected comprehensively according to different patients, different clinical stages, whether it is preoperative neoadjuvant chemotherapy or postoperative adjuvant chemotherapy. Patients should choose targeted chemotherapy programs under the guidance of professional doctors.